Drive diagnostics (MG1/MG2 - motor-generators)

Hybrid vehicles such as Toyota Prius and many Toyota and Lexus models use electric motor-generators known as MG1 and MG2 that work together with the gasoline engine and hybrid transmission. When problems occur the vehicle may show unstable transmission operation, jerking or shuddering during acceleration, harsh engagement, or the transmission may go into a fail-safe mode during hard acceleration. In many cases the dashboard will display a warning message such as "Check Hybrid System". Many owners assume the issue is related to the high-voltage battery, however after proper diagnostics and resistance testing of the motor-generator windings it is often discovered that one of the internal windings inside the hybrid transmission has failed. From practical experience in about 85% of cases this type of failure occurs because the transmission fluid has not been changed for a long time. Metal particles circulating in the fluid can accumulate on the motor windings and eventually cause an internal short circuit. Hybrid transmissions are very sensitive to fluid condition, which is why regular fluid service is important. Proper diagnostics allows the real cause of the problem to be identified before unnecessary and expensive repairs are performed.